Scaling analysis of the new multicritical behavior of CsMnBr3 and CsNiCl3.

Abstract

Critical properties of the axial triangular antiferromagnet ${\mathrm{CsNiCl}}_{3}$ and the planar triangular antiferromagnet ${\mathrm{CsMnBr}}_{3}$ under an applied magnetic field are studied using scaling theory. Novel types of multicritical behavior observed in these compounds are associated with n=2 (${\mathrm{CsMnBr}}_{3}$) and n=3 (${\mathrm{CsNiCl}}_{3}$) chiral universality classes recently identified by the renormalization-group analysis. Various experimentally testable predictions are derived on the basis of a scaling ansatz combined with the numerical estimates of critical exponents. In particular, all phase boundaries emanating from the multicritical points are found to be scaled by the corresponding anisotropy-crossover exponent. It is also predicted that the criticality along the high-field critical line of ${\mathrm{CsNiCl}}_{3}$ (paramagnetic to spin flop) is of n=2 chiral universality.